The first Landsat Earth Observation satellite was launched back in 1972; images of our planet's land have been acquired continuously since then. A major benefit of this long dataset is the ability to identify gradual changes occurring on the Earth's surface.
Twenty years separate these two Landsat Thematic Mapper (TM) images of Instanbul, the largest city in Turkey and the administrative capital of the Province of Istanbul. Until 1930 Istanbul was commonly known by its original Greek name Constantinople, and in Classical Antiquity as Byzantium or Byzantion. Today, with a population of between 11 and 15 million people, Istanbul is the most populated city of Turkey and is considered by some to be one of the largest cities in Europe. The old part of the city, which corresponds to ancient Constantinople, is mainly located on the south west corner of the Bosporus strait. However, the modern city is much larger and covers both the European and Asian sides of the Bosporus. The strait separates Europe from Asia and the Black Sea from the Marmara Sea. Two bridges cross the strait: the first, Bogazici (Bosporus I) bridge, was buit in 1973 and is visible only in the first image; the second, Fatih Sultan Mehmed (Bosporus II) bridge, was completed in 1988 about five kilometres north of Bosporus I. The comparison between the 1984 image on the left and the 2004 image on the right suggests that Istanbul has not undergone a substantial growth in the last 20 years. Most of changes have affected the western areas of the city. Here, the Atatürk International Airport, visible as the bright area by the coast of the Marmara Sea, on the centre left of both images, grew considerably from 1984 to 2004. Istanbul lies in one of the most seismic areas of the planet. The North Anatolian Fault, the most active fault system in Turkey, runs about 40 kilometres to the southeast of the city. One of the strongest (7.4 on the Richter scale) and most recent seismic event associated to this fault array is the Marmara earthquake. It occurred on August 17 1999 at 3:00 am (local time) and caused the death of more than 17,000 people. 44,000 were injured and damage to Turkey's industrial heartland was extensive.